An evaporative fuel processing apparatus includes a canister, which holds evaporative fuel evaporated in a fuel tank, a purge passage, which guides the evaporative fuel held by the canister to an intake air passage, and an electric purge valve, which opens and closes the purge passage (see FIG. 1).
Lately, a negative suction pressure generated in the intake air passage tends to be reduced because of a reduction of a displacement of an internal combustion engine, a reduction of a rotational speed of the engine due high-gearing of a transmission, use of a supercharger for energy saving or the like. When the negative suction pressure is small, a purge amount of evaporative fuel guided from the canister to the intake air passage is reduced, and thereby the purge process is deteriorated.
In view of the above disadvantage, there is proposed a technique of pumping the evaporative fuel held by the canister to the intake air passage through an operation of an electric purge pump installed in the purge passage (see, for example, JP3589632B2 corresponding to U.S. Pat. No. 6,196,202B1).
Lately, in the case of, for example, a hybrid vehicle or an idling stop vehicle, an operation of the internal combustion engine tends to be limited for the purpose of energy saving or reduction of CO2 emissions. Therefore, it is desirable to always guide evaporative fuel held in the canister to the intake air passage during the time of operating the engine. In such a case, the purge pump needs to be always operated during the time of operating the engine.
In order to meet this demand, it is desirable that the purge pump has a very long life and high endurance. This will result in an increase in the costs of the purge pump and also result in an increase in the electric power consumption due to the operation of the purge pump all the time during the time of operating the engine.
In order to address the above disadvantage, it is conceivable to drive the purge valve from a valve closing state to a valve opening state and starts an operation of the purge pump upon satisfaction of a predetermined purge condition. Specifically, as shown in FIG. 4, at the timing T, at which the purge condition is satisfied, the purge valve of normally closed type is turned on, and the purge pump is operated.
However, when the operation of the purge pump is started after the satisfaction of the purge condition, there will be a time lag from the time of starting the rotation of the purge pump to the time of reaching a rated rotational speed of the purge pump. Thereby, a response delay of the purge occurs. Furthermore, this response delay may cause a shortage of the purge amount of evaporative fuel.
The present disclosure addresses the above disadvantage. According to the present disclosure, there is provided an evaporative fuel processing apparatus that includes a canister, a purge passage, an electric purge valve, an electric purge pump and a control device. The canister holds evaporative fuel, which is evaporated in a fuel tank. The purge passage guides the evaporative fuel, which is held by the canister, to an intake air passage of an internal combustion engine. The electric purge valve is electrically driven to open and close the purge passage. The electric purge pump is installed in the purge passage and is electrically driven to pump the evaporative fuel from the canister to the intake air passage. The control device controls energization of the electric purge valve and energization of the electric purge pump. A condition for executing a purge process by opening the electric purge valve and driving the electric purge pump in a middle of operating the internal combustion engine is defined as a purge condition. A condition, which is satisfied before satisfaction of the purge condition in the middle of operating the internal combustion engine, is defined as a precondition. The control device starts an operation of the electric purge pump at a time of satisfying the precondition and opens the electric purge valve at a time of satisfying the purge condition.